Radiation therapy has long been used in medicine. Typically, high energy radiation from sources such as linear accelerators and radioisotopes is used, especially in whole-body, external beam systems where the radiation may need to penetrate a significant amount of tissue in order to reach the target volume and attain within the target volume the prescribed therapeutic dose level and fractionation scheme. The irradiation of normal tissue is a necessary physical consequence of all modes of radiotherapy and typically becomes the limiting factor in any given patient's therapy regimen. In procedures that use radiation sources inside the patient's body, a similar challenge is the undesirable but unavoidable exposure of normal tissue. Conventional, whole-body, external beam systems can be used for breast therapy as well but their large, whole body geometry tends to lead to undesirable irradiation of significant amounts of healthy tissue. Also, whole body, external beam systems may be designed to irradiate at energy levels that are not optimized for breast tissue. In order to reduce normal tissue irradiation and achieve sufficient target volume dose, efforts have been made to find other approaches for breast radiation therapy, leading to methods that include, in addition to the orthovoltage radiation treatment disclosed in said earlier-filed patent applications, proposals by others such as (1) internal breast brachytherapy which involves inserting catheters or needles in the breast and placing radioactive substances in or through the catheters or needles or using radioactively coated needles, (2) surgically implanting a balloon in the breast and selectively delivering radioactive material to the balloon through a catheter, (3) surgically positioning a miniature x-ray tube inside the breast, (4) external stereotactic brachytherapy that involves compressing the breast between two sets of conforming channels through which a radioactive substance is placed in close proximity to the breast, (5) using orthovoltage radiation from an external kilovoltage x-ray source that irradiates the breast from the side or possibly through a purposely designed surgical opening in the tissue, (6) using a LINAC radiation source that rotates in a horizontal plane to irradiate a downwardly protruding breast of a patient on a table with an opening for the breast, and imaging the breast with that source or an adjunct source, and (7) combining a radioactive substance with a biologically active material designed to uptake selectively in the breast tissue where it decays and provides a therapeutic dose (such as monoclonal antibodies) or a substance which causes the tumor to be more radiosensitive during the treatment.
An external beam radiation therapy treatment typically involves therapy planning in which the location and perhaps other characteristics of a lesion or other target volume or other tissue to be treated or avoided and monitored are identified by one or more imaging technologies such as ultrasound, X-ray computed tomography, static and dynamic planar imaging, nuclear medicine imaging, and magnetic resonance imaging. Information from these imaging modalities is used in computer processing to develop a treatment plan for the directions, energies, and durations of the therapy radiation beams and the number and frequency of the treatment sessions. In addition, before each radiation therapy session images of the lesion and/or other target volume or other tissue may be taken to check the position of the target volume and other tissue relative to the geometry of the radiation therapy system, and various positioning aids may be used in the therapy system to verify and maintain a desired geometric relationship between the radiation treatment beam(s) and the target tissue and possibly other tissue. Brachytherapy also typically involves similar treatment plan and verification procedures. Typically, the treatment plan and verification imaging is done on equipment physically separate from the radiation treatment equipment. Although care can be taken to preserve the position of the tissue of interest relative to frames of reference that pertain to both the imaging equipment and the treatment equipment, there is a risk that transferring the patient from one piece of equipment to another may disturb that relationship, with the result that the actual radiation treatment may not match the planned treatment.
See, for example, H. E. Johns & J. R. Cunningham. The Physics of Radiology, Ch. Thomas, 1983; S. C. Formenti, External-Beam Partial-Breast Irradiation, Seminars in Radiation Oncology, Elsevier 2005, 82-99; G. Jozsef, G. Luxton, S. C. Formenti, Application of radiosurgery principles to a target in the breast, A dosimetric study, Med. Phys. 27 (5). May 2000, 1005-1010; O. Gayou, D. S. Parda, M. Miften, Patient dose and image quality from mega-voltage cone beam computed tomography imaging, Med. Phys. 34 (2). February 2007, 499-506.
Despite such advances in radiation therapy systems, including for breast radiation, it is still desirable to improve breast radiation therapy by making it more effective and efficient.